1. Field of the Invention
This invention relates in general to an automatic control for bilge and sump pumps and in particular to a magnetically controlled pump.
2. Description of Related Art
Limit switches have traditionally been utilized on countless types of commercial bilge and sump pumps. The limit switch may be mounted within a hinged float and be energized by a rolling element which engages the switch actuator when the float has reached an angle that is sufficient for the rolling element. The pump will remain energized until the float has fallen to an angle which allows the rolling element to roll away from the switch actuator. There is a problem with this system in that the two electrical conductors penetrating the float must be sealed. Other limit switches that are commonly employed are enclosed in the pump motor sealed chamber. This requires a membrane or other means that will allow a pivoted or otherwise constrained float means to communicate its position to the switch actuator without allowing liquid to enter the sealed chamber. Such systems result in actuation and de-actuation levels which are variable due to added friction and tolerance buildup.
Mercury switches have been used within a hinged float instead of a limit switch and a rolling element. These structures have the same sealing problems and are less precise in the set points for controlling the pump as the float rises and falls with the liquid level. The liquid mercury exaggerates the tendency to false trigger the motor when in a dynamic environment such as a bilge pump in a small boat. Also, a pair of electrodes at both the beginning and end pumping liquid levels have been used with a logic circuit and a power relay that is energized when the upper pair of contacts close and remains energized until the lower pair of contacts is open. Problems occur such as maintaining conductivity of contacts which are intermittently submerged in a dirty, oily environment in which solids can be baked onto the contacts creating an insulating barrier. Both limit and mercury switch type controls must turn off the pump motor before the float bottoms or the motor would run continuously to destroy the motor or to exhaust the battery.
In a dynamic application such as the bilge of a small boat as the boat bounces from wave to wave, the pivoting float will cause the switch to close many times per minute even without water in the bilge. This needlessly consumes the switch contact so that the system has a relatively short life.
See also U.S. Pat. Nos. 3,316,845, 4,345,879, 4,917,135, 4,941,806, 5,025,827, 2,844,678, 3,999,890, 4,165,204, 4,186,419, 4,275,995, 4,805,066, and Design 306,447.